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GSM Standardisation andTechnology

Training Document


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GSM Standardisation and TechnologyThe information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been

prepared to be used by professional and properly trained personnel, and the customerassumes full responsibility when using it. Nokia Networks welcomes customer comments aspart of the process of continuous development and improvement of the documentation.

The information or statements given in this document concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered bindingbut shall be defined in the agreement made between Nokia Networks and the customer.However, Nokia Networks has made all reasonable efforts to ensure that the instructionscontained in the document are adequate and free of material errors and omissions. NokiaNetworks will, if necessary, explain issues which may not be covered by the document.

Nokia Networks' liability for any errors in the document is limited to the documentarycorrection of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FORERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL ORCONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use ofthis document or the information in it.

This document and the product it describes are considered protected by copyrightaccording to the applicable laws.

NOKIA logo is a registered trademark of Nokia Corporation.

Other product names mentioned in this document may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.

Copyright Nokia Oyj 2003. All rights reserved.


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Table of ContentsTable of Contents

1 Objectives ................................................................................... 4

2 Technologies .............................................................................. 52.1 Why Digital?................................................................................. 52.2 Standardisation ............................................................................ 52.2.1 European Telecommunications Standard Institute

(ETSI)........................................................................................... 5

3 GSM Overv iew ............................................................................ 7

4 Radio Access ............................................................................. 94.1 Multiple Access Techniques ........................................................ 9

4.2 Frequency Division Multiple Access (FDMA)............................... 94.2.1 Time Division Multiple Access (TDMA)........................................ 94.2.2 Code Division Multiple Access (CDMA)..................................... 104.2.3 Space Division Multiple Access (SDMA) ................................... 104.3 Channel Types........................................................................... 11

5 Modulation ................................................................................ 135.1 Modulation ................................................................................. 135.1.1 Complex Signals........................................................................ 135.1.2 Fourier Transformation .............................................................. 145.1.3 The Radio Engineers Dilemma ................................................. 145.1.4 GMSK Spectrum........................................................................ 15


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GSM Standardisation and Technology

1 Objectives

At the end of this module the participant will be able to:

Describe GSM architecture and main elements

List radio access technologies

Describe the principles of GMSK modulation


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2 Technologies

Second generation cellular systems on a fully digital basis are the systems

belonging to the GSM family. GSM900 and its twin sister GSM1800(formerly DCS1800) are in worldwide use in over 100 countries on all

continents now.

In the USA a GSM derivative (GSM1900) is being promoted as a competitor

to US-based CDMA (Code Division Multiple Access) systems. GSM1900 is

very similar to GSM900/1800, but uses a different voice coding system. This

is more a political issue rather than a technical issue.

2.1 Why Digital?During transmission through the entire communication chain signals become

distorted by noise, non-linearity in amplifiers, interference from other

transmitters, etc. Analogue signals may take any given waveform. Therefore

distortions are undetectable since any signal form is valid. Digital signals have

two distinct states, 1 and 0. At any intermediate stage, a digital signal can

be regenerated to its ideal state. Error correction algorithms can be applied to

detect transmission errors (bit errors). Such, a digital signal can be carried

clean all the way from source to destination and be converted to an audible

(analogue) signal only at the receiving users ear.

As opposed to analogue, digital signals can be: ideally and error-free regenerated

packaged

compressed

stored

reproduced identically

easily de-/ and encrypted

2.2 Standardisation

2.2.1 European Telecommunications Standard Institute (ETSI)

ETSI (European Telecommunications Standard Institute) was founded by the

former CEPT (Confrence Europene des Postes et Tlcommunications).


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ETSIs task is to elaborate unified standards for telecommunicationsequipment in Europe.

ETSI is financed by the European Union (EU) and contributions of its

members. It is a co-operation between all the major telecommunication

suppliers and operator companies.

Presently standards issued by ETSI include:

Cellular: GSM 900 (Global System for Mobile Communications), GSM

1800, GSM 1900, GPRS (Generalized Packet Radio Services), UMTS

(Universal Mobile Telecommunication System)

Cordless Telephony: DECT (Digital European Cordless Telephone)

Paging: ERMES (European Radio Messaging System)

Trunked Radio: TETRA (Trans-European Trunked Radio System)

ETSI is located in the Sophia Antipolis technology park (French SiliconValley) near Nice in Southern France.


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3 GSM Overview

The principle of the GSM System architecture is shown in the illustration

below:

other MSC

other BTSs

VLR HLREIR

AuCOMC

Figure 1. GSM architecture

A site (=BS) can have several sectors (=cell). Each sector consists of a

number of TRXs.


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Channel spacing 200kHz

Usual bandwidth values (GSM900):5 ..8 MHz per operator in one or more sub-bands

1880

GSM 900 :

25 MHz

GSM 1800 :

75 MHz 1710 1785 1805

duplex distance : 95 MHz

890 915 935 960


GSM 1900 :

2 x 60 MHz at channel spacing 200kHz = ~300channels

Band subdivided by FCC into subbands A..F

sub-bands A, B, C : 2 x 15 MHz spectrum

sub-bands D, E, F : 2 x 5 MHz

1850 1910 1930 1990


Figure 2. GSM frequency bands

GSM 900 and GSM 1800 are twins. There are no major differences betweenthem except the operating frequency:

GSM 900 GSM 1800

Frequency band 890...960 MHz 1710...1880 MHz

Number of channels 124 372

Channel spacing 200 kHz 200 kHz

Access technique TDMA/FDMA TDMA/FDMA

Mobile power 0,8 / 2 / 5 W 0,25 / 1 W


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4 Radio Access

4.1 Multiple Access Techniques

In order for several radio links to be in progress simultaneously in the same

geographical area without mutual interference, arrangements have to be made

to avoid system degradation due to mutual interference. This is known as

multiple access to a common transmission medium. Several multiple access

techniques exist:

Frequency Division Multiple Access (FDMA)

Time Division Multiple Access (TDMA)

Code Division Multiple Access (CDMA)

Space Division Multiple Access (SDMA)

4.2 Frequency Division Multiple Access (FDMA)

FDMA systems allocate one frequency band continuously (in time) to one

specific user, who is the only one transmitting and receiving on this

frequencies during his time of transaction. Each radio resource (radio channel)is identified with the carrier frequency and relative bandwidth. In the GSM

900-case the carrier frequencies are in the 900 MHz band and the single

channel bandwidth available for one user is 200 kHz.

4.2.1 Time Division Multip le Access (TDMA)

TDMA systems operate with time slots, short periods of time. Each user is

assigned to a specific timeslot for his transaction. Within a specific radio

channel (frequency channel) several users are served. They share the channel

sequentially in time. The time slots are of very short duration, the user,however, perceives a continuous speech stream due to appropriate

compression and expansion techniques at transmitter and receiver.

TDMA is the choice mainly in digital systems. From a bandwidth perspective,

FDMA and TDMA provide the same spectral efficiency (measured in kHz per

user). Figure 3 illustrates the TDMA principle.


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T = Allocated time

t

A

Slot for user 1

Slot for user 2

Slot for user 3

Slot for user 5

Slot for user 7

Slot for user 8

Slot for user 4

Slot for user 6

Figure 3. Time division multiple access principle

4.2.2 Code Division Multip le Access (CDMA)

CDMA follows the idea of many users using one single physical radio

channel (spread spectrum approach). Coding each stream with orthogonalcoding sequences separates user data streams. Orthogonality thereby provides

(ideally) a cross-correlation of zero; i.e. each stream can be extracted error-

free by correlation.

Multiplying each user data bit with a spreading sequence increases the used

bandwidth considerably (spread spectrum). Since the signals of all users are

by nature then co-channel interferers to any other users signals, resistance

against interference needs to be provided by the achievable coding gain of the

spreading sequence. More coding gain can be achieved by longer sequences,

which in turn increases the bandwidth used. Sets of orthogonal (cross-

correlation = 0!) and long sequences are difficult to find. A cross-correlation

other than zero means that the signal cannot be extracted uninfluenced byother signals, i.e. bit errors remain.

4.2.3 Space Division Multip le Access (SDMA)

SDMA follows the idea of separating users by their location in space (or in

angle). By transmitting and receiving signals only into the direction where the

user/basestation signals are coming from, interference to other users is


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reduced considerably. SDMA requires "smart"/adaptive antennas, which in

turn require a certain physical space. Therefore smart antennas are especially

to be deployed at the base station. SDMA is a technique which become

popular recently, but it still will take some time to be deployed in commercial

systems.

4.3 Channel Types

In mobile communications different types of physical radio channels can be

distinguished (see Figure 4):

Simplex channel:The generic channel type. A specific radio frequency is

allocated to each party (FDMA). The channel is permanently allocated to the

user. Usage: e.g. amateur radio, walkie-talkie

FDMA/TDD:(TDD Time Division Duplex) The same radio channel is

used alternatingly for direction A-to-B, then B-to-A, etc. Usage: e.g. cordless

phones (half-duplex channel)

TDMA/TDD:Timeslots on same radio channel are used for both uplink and

downlink direction. Usage: e.g. DECT

FDMA/ TDMA:A timeslot on a radio channel is allocated to a specific user.

Different users are on the same frequency channel and another timeslot or on

another frequency channel and another timeslot. There exist several frequency

channels in parallel. Uplink and downlink directions operate on different radio

frequencies (FDD Frequency Division Duplex). Usage: e.g. GSMCDMA/FDMA:Users on the same frequency channel are separated by

different codes. There exist several frequency channels in parallel. Uplink and

downlink directions operate on different radio frequencies (FDD). Usage: e.g.

UMTS


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A to B

B to A

f1

f2

f3f4

FDMA : e.g. walkie-talkie

A to B B to A A to B B to A

X to Y Y to X X to Y Y to X

C to D D to C C to D D to CM to N N to M N to M M to N

f1

f2

f3f4

FDMA/TDD : e.g. CT2-system

f1

f2

f3

f4

1 2 3 4 5 6 ... 1 2 3 4 5 6

TDMA/TDD : e.g. DECT

f1

f2

f3

f4

1 2 3 4 5 6 ... 1 2 3 4 5 6

3 4 5 6 ... 1 2 3 4 5 6 .. 1

FDMA/ TDMA: e.g. GSM

Figure 4. Channel types


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5 Modulation

5.1 Modulation

Regardless of the technology used, in radio link there is always a carrier

frequency, which is being modified by the information signal. There are

several ways to modulate the carrier. Regardless of the technology of the

information signal (analogue or digital), the result modulated carrier signalis always analogue.

Where is the information?

Amplitude modulation

Frequency modulation

Phase modulation

equidistant sampling points

Figure 5. Modulation types

5.1.1 Complex Signals

While unipolar or bipolar signals (0 / 1 or -1 / +1) can be displayed inone dimension, complex signals span out a signal plane (2-dimensional

signals). The distance of the signal point from the origin represents the signal

amplitude (energy); the angle of the sample represents the value of the

symbol. Such, multi-level signals can be represented with a single signal

sample. This pie-slices principle is referred to also as angular modulation.

In microwave radio links multilevel QAM signals are used, thereby providing

a very efficient modulation scheme. In mobile radio the transmission path


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GSM Standardisation and Technology(air) is very variant and unreliable, therefore on four signal points in the

complex plane are used to minimise error probability.

I

Q

I

Q

Multiplying the user data stream with two orthogonal signals generates

complex signals (simplest case: sine and cosine wave). By superposition of

both partial streams a complex (2-dimensional) signal is created.

For details on modulation schemes refer to theory books.

5.1.2 Fourier Transformation

In signal theory there is a duality of time and frequency. The Fourier

transform provides the means to equivalently transform a signal

representation in time domain into frequency domain and vice versa.

-3 -2 -1 0 1 2 3

k/a

w(x)

-3 -2 -1 0 1 2 3

k/a

w(x)

2 3 4-2-3-4 0

kx/a

W(kx)

2 3 4-2-3-4 0

kx/a

W(kx)

W k w x e dxxjk xx( ) ( )=

1

2

Figure 6. Fourier transformation

5.1.3 The Radio Engineers Dilemma

As seen from Fourier transform properties, an instant signal change in time

domain (e.g. a binary signal changing from 1 to 0) causes an infinite

signal in frequency domain. Since bandwidth of any system is strictly limited


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this means that any system with a certain bandwidth can only support a

certain modulation speed. In other words: bandwidth * modulation speed =

constant.

The radio engineers dilemma is that either we can have fast modulation ORnarrow bandwidth, but not both. Since we would like to optimise both

contradictory parameters, it seems well have to settle for a compromise,

allowingprettyfast modulation at an acceptablynarrow bandwidth.

5.1.4 GMSK Spectrum

In search of a modulation scheme providing an acceptable compromise of

both parameters, the GSM community has decided to use a Gaussian

Minimum Shift Keying (GMSK) modulation with properties B*T = 0,3.

The Gaussian stands for a filtered modulation signal with limited signalslopes (time domain), which in turn guarantees limited bandwidth in

frequency domain. Minimum Shift keying is a modulation scheme featuring

a continuous phase trajectory, i.e. no sudden jumps of the signal vector.

The combination of both allows GSM to perform at a modulation speed of

approx. 271 kb/s within a modulation bandwidth of 162 kHz (allowing a

channel spacing of 200 kHz)

Figure 7. Digital modulation spectrum


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Radio Propagation Channel

Training Document


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Radio Propagation ChannelThe information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been









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Table of ContentsTable of Contents

1 Objectives ................................................................................... 4

2 Reflections, Dif fract ions and Scattering.................................. 52.1 Calculation in dB.......................................................................... 52.2 Propagation Mechanisms ............................................................ 6

3 Mult ipath and Fading ................................................................. 73.1 Fading.......................................................................................... 8

4 Propagation Slope and Different Environments ................... 114.1 Propagation Loss....................................................................... 124.1.1 Plane Earth Approximation and Path Loss Breakpoint.............. 14


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1 Objectives


Describe basic propagation mechanisms

Describe multi path propagation

Describe the difference between fast and slow fading

Describe factors of path loss


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2 Reflections, Diffractions andScattering

2.1 Calculation in dB

Decibel (dB) is a relative, logarithmic scale commonly used in

communications theory. dB always refers to a reference value, e.g. the

isotropic radiator in antenna context (dBi) or militates in link budget

calculations (dBm). As a rule of thumb: 3 dB is linear factor 2, and 10 dB is a

linear factor of 10.

Calculations in dB (deci-Bel) logarithmic, relative scale

Always with respect to a referencedBW : dB above Watt

dBm : dB above mWatt

dBi : dB above isotropic

dBd : dB above dipole

dBV/m: dB above V/m

rule-of-thumb: +3 dB = factor 2

+7 dB = factor 5

+10 dB = factor 10

-30 dBm = 1 W-20 dBm = 10 W-10 dBm = 100 W-7 dBm = 200 W-3 dBm = 500 W 0 dBm = 1 mW

+3 dBm = 2 mW

+7 dBm = 5 mW

+10 dBm = 10 mW

+13 dBm = 20 mW

+20 dBm = 100mW

+30 dBm = 1 W

+40 dBm = 10W

+50 dBm = 100W

Power

Voltages

Conversion factorE(dBV/m) = P(dBm) + 106,4 + antenna factor

antenna factor = 20 log(f [MHz]) -29,8 - ant_gain + cable_lossantenna factor for

900 MHz : ~ 29 dB1800 MHz : ~ 35 dB

dBP

PPlin

P dB

=

=10 10

0

10log [ ].( )

dBE

EElin

E dB

=

=20 10

0

20log [ ].( )


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Radio Propagation Channel2.2 Propagation Mechanisms

Free- space propagation

Signal strength decreasesexponentially with distance

specular reflection

diffuse reflection

Reflection

Specular Reflection

amplitude: A --> *A (< 1)

phase : --> -

polarisation: material dependant phase shift

Diffuse Reflection.amplitude: A --> *A (< 1)

phase : --> random phase

polarisation : random

D

Absorption

heavy amplitudeattenuation materialdependant phase shiftsdepolarisation

Diffraction

wedge- model

knife edge

multiple knife edges

A A - 5..30 dB

Figure 1. Propagation mechanisms


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3 Multipath and Fading

The radio channel is reciprocal in field-strength. This means that a signal

propagating from A to B will experience the same path losses and attenuationwhen propagating from B to A. This is an important fact to remember when

considering link budgets. Reciprocity is true for field-strength, but not for

interference conditions. These may be greatly different at the mobiles

location as opposed to the base station location.

The mobile radio channel features time dispersion as a result of multipath

propagation. Partial signals take different paths to the mobile and

consequently arrive with different time delays in the order of some

microseconds. At velocity of light (c = 3 10^8 m/s) 1 sec delay correspondsto a path difference of approx. 300m.

GSM specifies an equaliser with a time window of 16 sec to be used in thereceiver. This means that all partial waves arriving within this time windoware valid contributions to the received signal. Signals with excessive delay act

counter-productive as co-channel interference.

Equalisers are specified to cope with standardised delay profiles

TU3: typical urban environment at 3 km/h (pedestrians)

TU50: typical urban at 50 km/h (cars)

HT100: hilly terrain at 100 km/h (road vehicles)

RA250: rural area at 250 km/h (highways, trains)

Note that there is no hard limitation at the speed of 250 km/h (130 km/h forGSM1800), despite of some discussions on this topic. Bit error rates may

under certain conditions exceed the specifications at higher speeds, but this

does not necessarily cut the connection. The limit --if at all-- is a very soft

limit. In fact, GSM900 has been successfully performing within specification

at speeds above 400 km/h and a German operator has conducted performance

tests of GSM1800 in high-speed trains travelling at 250 km/h.


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equaliser window 16 s

amplitude

delay time

echos

direct path

Figure 2. Equaliser window

3.1 Fading

There are several fading mechanisms to be distinguished in mobile radio

environment:

Slow fading:This is due to shadowing by terrain structures and large

obstacles. It is in the order of 10s of wavelengths. The slow fading can be

described mathematically by the Gaussian distribution.

Figure 3. Gaussian distribution

Rayleigh or fast fading:This phenomenon is due to multipath propagation of

the signal. Signals with same amplitudes and opposite phase shifts

superimpose and eliminate each other. This creates local very distinguished

fading dips in the order of fractional wavelengths. The Rayleigh fading


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process is applicable to obstructed propagation paths (non-line-of-sight

conditions) and can be mathematically modelled by the Rayleigh distribution.

Figure 4. Rayleigh distribution

Rician fading:This is a combination of the upper two conditions: Rayleigh

fading in the presence of a direct (line-of-sight wave). The ratio of direct to

indirect signal energy is the Rice factor. This fading type is applicable to

partly obstructed propagation paths. It is modelled mathematically by the

Rician distribution

K = 0

(Rayleigh)

K = 1

K = 5

Figure 5. Rician distribution, K = 0:Rayleigh; K >>1: Gaussian

In mobile environment the received signal generally is not received via the

direct line-of-sight path (which often doesnt even exist), but by a variety of

different independent propagation paths (multipath propagation).

The received signal can be seen as a superposition ofseveral superimposed

individual partial signals having a certain amplitude and phase (complex

signals). Each partial signal corresponds to a certain propagation path. Each

signal has experienced several reflections and diffractions, each causing


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Radio Propagation Channelamplitude attenuation and a random phase shift. The resulting signal vector is

composed by vector addition of its components, see Figure 6. In every instant

the partial waves take different (complex) values, thereby also influencing the

resulting vector.

A1

A2

A3

A4

A5

Aresult

1

2

3

4

5

result

Figure 6. Phasor diagram


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4 Propagation Slope and DifferentEnvironments

It can be easily shown that in free space signal power decreases with the

square of distance from the antenna. This simplified illustration shall explain

the basic mechanism:

Free space loss proportional to 1/ d^2Simplified case: isotropic antenna

Which part of total radiated power is foundwithin surface s ?

Simplified case (perfectly isotropic antenna) :Power density = P / Stotal power within surface s : P = P/S *s

assume R=100m: ==> P = P/ 7,96*10e-6==> -51 dB

(coupling loss at ref. distance)

Power density reduces with square of distance==> received power per area unit reduces at same rate==> free space loss proportional to 1/d^2

R

Surface S = 4* R^2

assume surface

s = 1m^2

2d

4d

A = 4*A

A = 16*A

A

d

Figure 7. Free space loss

Radio wave signals attenuate with the square of distance in the best case. This

is pure law of physics and valid for all frequency bands and modulation types.

In mobile communication, signal levels decrease with 3rd to 4th power of

distance, depending on terrain.

Signal attenuation is often expressed in dB per decade or dB per octave

(meaning: doubling the distance). A decade has 3.32 octaves (Solve equation:

2 ^x = 10).


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Radio Propagation Channel Power density by the

receiving end:

Effective antennaarea:

Received power

Mobile environments: )5...5,2( == withdCGGPP rssr

Reff GA

4

2

=

Pr= S Aeff

SP G

d

s s=4

2

P

P G G d

r

ss r=

4

2

Ps

As

Gs

Pr

Ar

Gr

d

2

4

Figure 8. Signal propagation formulas

In radar technology received power is inversely proportional to the 4th power

of distance, since the signal traverses distance twice.

In mobile communications distance is traversed only once, but the

propagation path is not free-space (line-of-sight), but heavily obstructed in

most cases, causing considerable loss. Received signal levels are inversely

proportional to the 2nd ...5th power of distance, depending on the

environment between transmitter and receiver.

4.1 Propagation Loss

Radio wave propagation losses are usually calculated in a logarithmic scale, in

dB. Losses are exponential with distance. Propagation loss formulas are based

on the free-space loss formula with additional empirical correction factors.


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Bas ic los s formula

C lutte r loss fac tors land-usage classesus ually stated in dB /deca dee.g. :

L L d= +0 log( )

loss at reference point (e.g. 1km)

losses are exponential with distance

free s pace 20 dB /dec

ope n countrys ide 25 dB /de c

suburban areas 30 dB /dec

urban area 40 dB /dec

h is to ric c ity c entre >45dB/dec

0,1km 10km1km

EIRP level

coupling loss

= L0

reference

distance

20 dB/dec

30 dB/dec40 dB/dec

Figure 9. Propagation loss

Signal levels attenuate differently in different environment (land usage

classes). Typical signal attenuation rates are 20 ..45 dB/decade.

25 dB/dec

30 dB/dec20 dB/dec

40 ..50 dB/decpath l

Figure 10. Signal attenuation in different environments

The radio signal attenuation depends on the environment the signal passes

though. A rise in signal strength can be observed despite of increasing

distance, when the receiver re-enters open area after passing through urban

environment, causing a higher attenuation exponent. Since the received signal


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Radio Propagation Channelstrength depends on the close environment of the receiver, there is no abrupt

rise in signal strength but a gradual increase, as the mobile enters open area.

urban: 40 ..50 dB/decopen: 25 dB/dec open: 25 dB/dec

open area curveurban curve

actualsignal level

signallevel

distance

Figure 11. Mixed path loss

4.1.1 Plane Earth Approximation and Path Loss Breakpoint

The so-called plane earth approximation is used for studying radio wave

propagation mathematically. In this approximation, the earth is assumed to becompletely flat and smooth. Hence, the received signal is a result of exactly

two signals; the direct (LOS) signal and once ground-reflected signal, see

Figure 12.These signals sum up constructively or destructively, depending on

their phases. The phases of the received signal components depend on the

path length differences and reflection coefficient. For very small angles of

incidence (measured from the ground) the reflection coefficient is 1 for both

polarisations, hence the two signals tend to compensate each other as distance

increases. This leads to a path loss exponent of 4 after a certain distance. This

distance is called "the breakpoint distance".


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Figure 12. Propagation over plane earth

The formula for break point distance calculation is

,4 21

hhB =

where h1and h2are the transmitting and receiving antenna heights.

Real environments are, of course, totally different from the plane earth

approximation. However, in practical field strength measurements a path loss

breakpoint is usually really detectable. If one would be able to determine the

path loss breakpoint exactly, it would be a great benefit in network planning;

the serving cell would be the region up to the breakpoint distance and less

interference would be generated for the other area.


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Radio Network Planning Process

Training Document


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The information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been









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Table of Contents

Table of Contents

0 Objectives ................................................................................... 4

1 Introduction and Pre-planning .................................................. 51.1 Network Planning Competence ................................................... 51.2 Network Characteristics............................................................... 51.3 Scope of Network Planning.......................................................... 61.4 Cellular Planning Process............................................................ 61.5 Input Data for a Planning Process ............................................... 81.6 Key Dimensioning Quantities....................................................... 9

2 Detailed Planning ..................................................................... 102.1 Coverage Planning .................................................................... 102.1.1 Coverage Planning Process ...................................................... 102.2 Coverage Requirements ............................................................ 11

3 Site Select ion ........................................................................... 133.1 Site Locations ............................................................................ 133.1.1 Bad Site Location....................................................................... 133.1.2 Good Site Location .................................................................... 133.1.3 Site Selection Criteria ................................................................ 143.2 Site Building Process................................................................. 153.3 Site Information.......................................................................... 15

4 Post -Planning ........................................................................... 17

5 Documentation ......................................................................... 18

6 Signal Measurements .............................................................. 196.1 Measurement Types .................................................................. 196.1.1 Measurement Methods .............................................................. 196.1.2 Choice of Routes ....................................................................... 206.1.3 Interpretation of Results............................................................. 20


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1 Objectives


Describe the radio network planning process

Describe the major tasks in the planning process

Describe the planning tools for the different phases

Describe the input and output documents (data)

Describe the planning environment


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2 Introduction and Pre-planning

2.1 Network Planning Competence

Traditional network operators (old PTTs) tend to do their very own network

planning following their internal structures. The advantage is detailed

knowledge of their network; disadvantages are often low efficiency and no

up-to-date knowledge of new techniques and features.

New network operators often come from a non-telecom background and

have no or little resources capable of doing network planning. Therefore this

task is often subcontracted to other companies.

Some infrastructure suppliers also offer network planning in more or less

detail. They usually require the use of their own equipment and have good

knowledge of internal limitations and undocumented features of the

equipment.

Many consulting companies also offer network planning services. Their main

advantage is independence from manufacturers. This makes them the natural

choice for operators in the license-tendering phase. It is difficult for

consulting companies to stay up-to-date with the latest information

concerning equipment capabilities of different suppliers.

2.2 Network Characteristics

Each operators network will have different characteristics. These strategic

intentions of the operator shall also be reflected in the network topology in

order to tailor a network according to the needs. The first operator in a

country could for example aim for plain coverage, whereas the second

operator could target for competitive pricing. The strategy of the third

operator could be replacing the wireline phones.

The following factors should also be taken into account when making the

planning:

Expected roamer numbers and locations

Existing international regulations at border areas

Are microwave links or leased lines the preferred solution?

Each network philosophy calls for a different planning approach.


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2.3 Scope of Network Planning

Network Planning is a complex task involving interactions with many

different functions within the operators organisations. Some tasks areiterative, therefore rather time and resource consuming.

Figure 1 shows the main dependencies and interactions within the scope of

network planning.

Network planning team

data acquisition

site survey and selection

field measurement evaluation

NW design and analysis

transmission planningNetwork design

number and configuration of B Santenna systems specificationsBS S topologydimensioning of transmission lines frequency plan

network evolution strategy

Network performance

grade of service (blocking)outage calculations interference probabilities

quality observation

Customer requirements

coverage requirementsquality of service recommended sites subscriber forecasts

External information sources

topo- & morphological datapopulation databandwidth available frequency co-ordination

constraints

Interactions with

external subcontractors

site hunting teams

measurement teams

operator

switch planning engineers

Figure 1. Scope of network planning

2.4 Cellular Planning Process

Coverage planning is an iterative and time-consuming task. It involves rounds

of discussions and decisions with site acquisition people. Figure 2belowshows the main process stream.


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external inputs:(traffic, subs. forecast,coverage requirements...)

Initial NW dimensioning

TRX?, cells, sites

bandwidth needed NW topology

nominal cellplansuggestions for

site locations cell parameters

coverage achieved

coverage prediction

signal strength

multipath propagation

Sitepre-validation

site inspection

site accepted ?

real cellplanfield measurements

planningcriteria fulfilled?

N

N

N

create cell

data forBSC

go tofrequencyplanning

field measurements

Figure 2. Coverage planning

Inputs from operators marketing and business planning departments are

considered for the initial network design. Then follows the very iterative

process of coverage planning. Aim of the transmission plan is to minimise the

costs for transmission over the networks life cycle. This then decides the

final network topology.

Frequency and interference calculations are iterated to the stage of acceptance

from the customer. This includes detailed inputs about traffic volumes anddistributions expected in the network.

Parameter planning and tuning increases the network performance.

Figure 3. Cellular planning process

CoveragePlanning andSite Selection

CoveragePlanning andSite Selection

ParameterPlanningParameterPlanning

PropagationmeasurementsCoverageprediction

SiteacquisitionCoverageoptimization

PropagationmeasurementsCoverageprediction

SiteacquisitionCoverageoptimization

External InterferenceAnalysisExternal InterferenceAnalysis

NetworkConfigurationandDimensioning

NetworkConfigurationandDimensioning

PRE-PLANNING

DETAILED PLANNING

Traffic distribution

Service distributionAllowed blocking/queuingSystem features

IdentificationAdaptationIdentificationAdaptation

Area / Cellspecific

Handoverstrategies

Maximumnetworkloading

Other RRM

NetworkOptimizationNetworkOptimization

POST-PLANNING

Surveymeasurements

Statisticalperformanceanalysis

QualityEfficiencyAvailability

Capacity Requirements

Requirementsand strategyfor coverage,quality andcapacity,

per service


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marketing

business

plan

traffic

assumptions

initial NW

dimensioning

freq. & inter-

ference plan

transmission

plan

final NW

topology

parameter

planning

coverage

plan

Figure 4. Cellular planning principles

2.5 Input Data for a Planning Process

Demographic Data:Demographic data are useful for estimating traffic

densities and distributions. Population distributions are valuable information

for placement of base stations, probable routing possibilities for terrestrial

lines etc.

Topographic Data: Before starting the coverage planning task, some

elementary topographic data need to be collected to get a first impression of

the countrys characteristics. Useful sources of data are a close study of maps

and local knowledge obtainable from residents.

Map informationincludes e.g.

location of main cities

important roads

location of mountain ranges

inhabited area

shore lines

Local knowledgeincludes

typical formation of city skylines

typical building architectures used

structures of city

local peoples habits (phone habits, normal working hours,

conversation styles...).


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2.6 Key Dimensioning Quantities

Some essential dimensioning figures for network design include:

number of base stations needed for coveragereasons

number of base stations needed for trafficreasons

acceptable outage probabilities

balance of interference level and acceptable frequency re-use rate

bandwidth available

Note that design goals are interdependent. A network can only be optimised

with respect to a single parameter. The overall optimum is always a trade-

off and compromise between different aspects.

Design goals and rules must be clearly agreed with the customer beforestarting the planning procedure.


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3 Detailed Planning

3.1 Coverage Planning

Coverage planning is the first (and also most visible) step in the actual

network planning process.

3.1.1 Coverage Planning Process

The coverage planning process is a major portion of network planning. Itinvolves several iteration loops with respect to site selection, site negotiation

and measurements. Coverage Planning is a quite resources and time-

consuming task.

external inputs:(traffic, subs. forecast,

coverage requirements...)

Initial NW dimensioning

TRX?, cells, sites

bandwidth needed

NW topology

nominal cellplansuggestions for

site locations

cell parameters

coverage achieved

coverage prediction

signal strength

multipath propagation

Site

pre-validation

site inspection

site accepted ?

real cellplanfield measurements

planning

criteria fulfilled?

N

N

N

create cell

data for

BSC

go to

frequency

planningfield measurements

Figure 5. Coverage planning process


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3.2 Coverage Requirements

The early and clean definition of coverage requirements is a fundamental

basis for network planning. This, of course, is on the traditional borderline oftechnical and marketing departments. Experience shows that this border is

seldom trespassed. However, the operators that have functioning co-operation

between technical and marketing staff are also the more successful operators.

The agreed targets should include:

Roll-out phases & time schedules

Coverage level requirements, i.e. coverage thresholds

Agree on min. levels for outdoor coverage

Indoor coverage area

Mobile classes to plan for

Operators cell deployment strategies

Omni-cells in rural areas?

3-sector cells in urban areas?

Minimum of 2 TRX per cell?

phase 1

NW launch

rollout

phase 2

rollout

phase 3

Figure 6. Rollout phases

Coverage thresholds affect the cell size as shown in Figure 7.In a hilly area

the surrounding mountains have more effect on the cell size than what the

coverage thresholds do.


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Figure 7. Coverage thresholds define the cell range in a flat open area

Full coverage of an area can never be guaranteed. Outages (see Figure 8)due

to coverage gaps and interference will always occur. The total location

probability in a cell is a function of the probability for no coverage and

interference:

(1- Pno_cov) * (1- PIf)Common values for the total location probability are between 90%-95% (time

and location probabilities).

Pno_covPif

Figure 8. Outage areas


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4 Site Selection

4.1 Site Locations

Proper site location determines usefulness of its cells. Sites are expensive,

long-term investments. Site acquisition is a slow process and hundreds of sites

are needed per network. Hence a base station site is a valuable long-term asset

for the operator. That's the reason that planners need to visit each site.

4.1.1 Bad Site Location

Hilltop locations for BS sites should be avoided as they cause:

uncontrolled interference

interleaved coverage

awkward HO behaviours

but: good location for microwave links!

wanted cell

boundary

uncontrolled, strong

interferences

interleaved coverage areas:weak own signal, strong foreign signal

Figure 9. Bad site location

4.1.2 Good Site Location

Sites off the hilltops are preferable as:

hills can be used to separate cells


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contiguous coverage area

only low antenna heights are needed if sites are slightly elevated above

valley bottom

wanted cell

boundary

Figure 10. Good site location

4.1.3 Site Selection Criteria

Radio criteria for site selection:

good view in main beam direction

no surrounding high obstacles

good visibility of terrain

room for antenna mounting

LOS to next microwave site

short cabling distances

Non-radio criteria for site selection:

space for equipment

availability of leased lines or microwave link

power supply

access restrictions?

house owner

rental costs


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4.2 Site Building Process

issue search area

& requirements

find suitablesite candidates

calculate coverage range

of each candidate

propagationmeasurements

needed ?

transmission

links available? sign contract

with site owner

get building permit

construction work

installing & testing

on air!

Figure 11. Site building process

Site acquisition is a slow process and hundreds of sites are needed per

network. Hence a base station site is a valuable long-term asset for theoperator. Therefore it is important to select good sites. They cannot be

changed easily.

4.3 Site Information

Collect all necessary information about site details. The necessary information

should include:

site co-ordinates, height above sea level, exact address house owner

type of building

building materials (photo)

possible antenna heights

360 degree photo (clearance view)

neighbourhood, surrounding environment


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drawing sketch of rooftop

antenna mounting conditions

access possibilities (truck?, road, roof)

BS location, approximate feeder lengths.


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5 Post-Planning

In post-planning verification, monitoring and optimisation tasks are carried

out in order to reach maximum capacity and quality from the radio network.


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6 Documentation

All the information that is needed to rebuild a site has to be documented to a

site folder database. Also measurement results and e.g. traffic history shouldbe documented.


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7 Signal Measurements

7.1 Measurement Types

Signal measurements can be divided into three different types. The different

types have different goals and are used in different phases of network

planning and optimisation.

7.1.1 Measurement Methods

Propagation measurements:

Purpose:

check coverage area of site

propagation model tuning

site candidate evaluations

Method:

test transmitter, mast, omni/directional antennas

CW- signal

Time:

planning phase

Functional test:

Purpose:

after commissioning of site, verify complete BS installation (incl.

antennas)

verify basic parameter settings (HO, power control )

Method:

coverage audit, real antenna types, ant. directions & tilting

use test mobile to check settings & record results

Time:

pre-opening phase


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Performance measurements:

Purpose:

check the users perspective of live network performance

secondary input to OMC information

identify problem areas in network

Method:

drive tests

real network under live conditions

Time:

commercial phase

7.1.2 Choice of Routes

Propagation measurements

stay within coverage area of cell

model tuning: preferably stay within a single land usage class

Functional tests

radial from site into neighbouring cells

check handovers in & out of cell

Performance measurements

define a random route once

drive repeatedly (comparable results!)

7.1.3 Interpretation of Results

Propagation measurements

signal averaging

Lees criterion: min. 50 samples per 40

estimate accuracy of prediction

database resolution

model tuning

Functional tests

identify incorrect parameter settings

check missing HO relations


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Performance measurements

detect misbehaviour of network

calculate call success rate

key performance indicators

evaluate network behaviour under nominal conditions (subscribers

view).


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Configuration Planning

Training Document


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The information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This document is intended for theuse of Nokia Networks' customers only for the purposes of the agreement under which thedocument is submitted, and no part of it may be reproduced or transmitted in any form ormeans without the prior written permission of Nokia Networks. The document has been









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Table of Contents

Table of Contents

1 Objectives ................................................................................... 4

2 Network elements ...................................................................... 52.1 GSM Elements............................................................................. 52.1.1 Base Transceiver Station (BTS) .................................................. 62.1.2 Nokia BTS.................................................................................... 72.2 Antenna Systems....................................................................... 132.2.1 Far Field Distance...................................................................... 132.2.2 Antenna Types........................................................................... 142.2.3 Antenna Characteristics............................................................. 152.2.4 Coupling Between Antennas...................................................... 182.2.5 Installation Examples................................................................. 182.2.6 Nearby Obstacles Requirement................................................. 192.3 Diversity Techniques.................................................................. 222.3.1 Space Diversity.......................................................................... 232.3.2 Polarisation Diversity ................................................................. 242.3.3 Combining.................................................................................. 242.3.4 Coverage Improvement by Diversity?........................................ 252.4 Antenna Cables ......................................................................... 252.5 Filters and Combiners................................................................ 262.6 MHA and Booster....................................................................... 292.6.1 Masthead Preamplifier (MHA).................................................... 292.6.2 Downlink Booster (TBU) ............................................................ 302.7 Base Station Controller (BSC) ................................................... 30

2.7.1 Nokia BSC ................................................................................. 322.8 Transcoder Submultiplexer (TCSM2E)...................................... 322.9 Mobile Switching Center (MSC)................................................. 332.10 Operation and Maintenance Center (OMC)/ Network

Management System (NMS)...................................................... 33

3 Power Budget........................................................................... 343.1 Link Budget Basics .................................................................... 343.2 Power Budget Factors ............................................................... 353.2.1 Power Budget Powers ............................................................... 363.2.2 Power Budget Receiver Sensitivities ......................................... 363.2.3 Power Budget Loss Factors....................................................... 36

3.2.4 Power Budget Gain Factors....................................................... 383.2.5 Power Budget Calculation.......................................................... 38


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1 Objectives

At the end of this module, the participant will be able to:

List the different elements used in the GSM network.

Calculate the power budget.

Describe how to balance uplink and downlink directions in the power

budget.


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2 Network elements

2.1 GSM Elements

Terminals are mostly hand-held, lightweight offering voice & data services.

Today (1999) the majority of users utilizes only voice services.

The SIM card holds all subscriber relevant information: identities, codes,

algorithms needed to identify the subscriber towards the network. The SIM

card is issued by the operator and may be transferred between mobiles, which

in turn then take the properties and access rights as defined on the SIM card.

Antennas are the most visible element of the infrastructure chain. Dependingon site configuration, 1..6 antennas are needed per site. Antennas increasingly

cause discussions about possible health hazards of mobile phones. To avoid

unnecessary spreading of this kind of "electrophobia", antennas should be

placed inconspicuously, hidden as much as possible from public view.

Antennas can be e.g. integrated into house facades or as a minimum the

antenna case can be painted in the same colour as the background.

Base Stations are the actual counterpart to the users mobile in terms of radio

transmission and reception. Base Stations are becoming increasingly more

compact in size. Presently BS are approx. the size of a TV-set. BS come as

outdoor or indoor versions in ranges from typically 2..12 TRX.

The Base Station Controller (BSC) controls radio resources and handoverfunctions of its associated base stations. Typically some 50 ...100 BS are

connected to a BSC, depending on network topology and the operators

design philosophy.

The Mobile Switching Center (MSC) is the termination point for all protocols

between mobile station and the network. The MSC performs all routing, call

control functions, Supplementary Services and provides connection to

external networks (Gateway-MSC)

The Base Station Subsystem (BSS) as defined in GSM, consists of the Base

Transceiver Stations (BTS's), the Base Station Controller (BSC) and the

Transcoder (TC) unit. The transcoder is usually physically located at the MSC

site, logically it belongs to the BSS. This physical separation has the

advantages that the transmission lines (typically many 10 km) between BSC

and Transcoder can be used much more efficiently (by factor 3..4) when voice

signals are transported in the compact GSM format, before being expanded

into the normal ISDN-type format in the transcoder. This brings great savings

in transmission resources.


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2.1.1 Base Transceiver Station (BTS)

The main tasks of a BTS are presented in Figure 1.

Base station transceiver maintain synchronisation to MS

GMSK modulation

RF signal processing (combining,filtering, coupling...)

diversity reception

radio interface timing detect access attempts of

mobiles

de-/ encryption on radio path

channel de-/ coding & interleaving on radio path

perform frequency hopping

forward measurement data to BSC

typ. 1..4 TRX1..3 sectorsavg. 7,5 traffic channels per TRXsupports typ. 300 users

typ. 1..4 TRX1..3 sectorsavg. 7,5 traffic channels per TRXsupports typ. 300 users

Figure 1. Tasks of BTS

Main entities of a BTS are

Transmitter and receiver unit

Frequency Hopping unit

RF combiners and filters

Signal processing units, channel coding, demodulation...

Alarm collecting units, clocks and timing

OMU: remote operation and maintenance transmission interfaces towards Abis interface

Power supply, heat exchangers....

See BTS product documentation for more details.


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2.1.2 Nokia BTS

Nokia base stations have different generations: Talk-family base stations (see

Figure 2)are the 3rd

generation base stations. PrimeSite and MetroSite are 4th

generation base stations.

Citytalk6 TRX

Extratalk, SiteSupport System

Flexitalk2 TRX

Flexitalk+2 TRX

Intratalk6 TRX

Figure 2. Talk-family base stations

FlexiTalk

Nokia FlexiTalk (MiniSite) is a 3rd

generation base station with 1-2 TRX in

one cell. It can be mounted on a wall, on a free-standing plinth indoors, or at

street level. The physical size of the base station is about equal to a television

set: 0,51m x 0,59m x 0,50m (hx wx d), weight 40 kg. The max TX output

power is 20 W.

FlexiTalk can be used in microcells, especially when indoor penetration and

coverage is needed. There is an option for fixed line transmission but no

possibilities for microwave radios without a cabin.

1-2 TRX omni

AC or DC power supply

Up to 3 coaxial or twisted pair 2M links

Support for Nokia microwave radio

Portable Site Test Monitor

Temperature range -5C to +45C


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FlexiTalk +

1-2 TRX omni



Support for Nokia microwave radio

Portable Site Test Monitor

Temperature range -33C to +40C plus solar load

20C to +40C (DC powered) plus solar load

IntraTalk

IntraTalkis the indoor version of the Talk-family BTS. It offers from 1-6

TRX omni or up to 6+6 or 4+4+4 in a sectored configuration. The base station

size is 1,60m high, 0,6m wide and 0,48m deep. Empty weight is 132 kg.

Omni directional 6 TRX and sectored up to 4+4+4 TRX

Integrated radio links


HDSL, ISDN


Redundant common unit power supply

Site Test Monitor

Temperature range -5C to +45C


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CityTalk

CityTalkhas been designed primarily for outdoor environments and rooftop

installations. The cabinet is small enough to be transported within buildings,

through standard size doors and in elevators (height: 1,36m, width: 0,77m,

depth: 0,88m, weight: 102kg). Two versions are available; the standard

cabinet with heat exchanger and the all climate cabinet with air conditioner.

Like the Nokia Intratalk, the first cabinet has a capacity up to 6 TRX with the

extension cabinet taking the BTS up to its maximum of 12 TRX.

Omni directional 6 TRX and sectored up to 4+4+4 TRX

Close-circuit internal airflow

Integrated radio links


HDSL, ISDN


Redundant common unit power supply

Site Test Monitor


ExtraTalk, Site Support System, support extension

Space for Line Terminal Equipment

19, 20U height sub-rack

Applications

IntraTalk, CityTalk and FlexiTalk

Alone or co-located with AC/DC or AC/AC cabinet


ExtraTalk; Site Support System AC/DC

Battery back-up

AC input, DC output

Typical back-up time 1 hour (tri-sector 1+1+1 TRX)

Redundant rectifier



Applications

IntraTalk, CityTalk and FlexiTalk


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ExtraTalk, Site Support System AC/AC

Battery back-up

AC input, AC output

DC feed for Line Terminal Equipment

Typical back-up time 1 hour (tri-sector 1+1+1 TRX)



Applications

IntraTalk, CityTalk, FlexiTalk and PrimeSite


PrimeSite

Figure 3. PrimeSite

PrimeSiteis a compact base station with 1 TRX. It includes an integratedcircularly polarised antenna, but there is a possibility for an external antenna.

The physical size of the base station is 0,65m x 0,38m x 0,14m (hx wx d),

weight 23 kg. The base station can be installed on a wall or pole. The

maximum transmitting output power is 8 W; therefore PrimeSite is useful in

microcells with high transmitting powers and relatively low capacity. It can be

used to fill coverage gaps or to provide indoor coverage and capacity.


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MetroSite Concept

MetroSiteis a new concept for microcells, including all equipment needed for

a microcell site: base station, (microwave) radio transmission equipment,

transmission node and a battery backup, see Figure 4.MetroSite suits

networks, where microcells with low transmission powers and very high

capacity are required.

MetroSite Base Station, MetroHub transmission node and MetroSite battery

backup have in addition to the same physical appearance also the same

mounting options and kits for vertical and horizontal wall mounting and pole

mounting.

Nokia MetroSite

Base Station

Connected to FXC RRI or

FC RRI indoor unit.

Connected to FXC RRI or

FC RRI indoor unit.

Nokia

MetroHopper Radio

Nokia MetroHub

Transmission Node

Nokia FlexiHopper

Microwave Radio

Nokia MetroSite

Battery Backup

Nokia MetroSite

Antennas

Figure 4. MetroSite concept

MetroSite Base Station is the core element of the MetroSite solution. It has 1-4 TRX, which can be freely divided to any combinations of omni or sectored

cells. It can be used in GSM 900, GSM 1800, GSM 1900 systems or as a

GSM 900 / GSM 1800 Dual Band base station. The base station is small:

0,84m x 0,31m x 0,22m (hx w x d) and relatively lightweight: 40 kg.

Therefore it is likely to make site acquisition and implementation easier.

Maximum transmitting power is 1 W. There are no internal combiners in the

base station. Base station supports RF hopping and later on also baseband

hopping. MetroSite BTS is easy to set up with the new autoconfiguration


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feature and the commissioning wizard of the MetroSite Manager local

management tool.

As the transmission media, microwave radio, fixed lines or 58 GHz radio can

be used with Nokia MetroSite BTS. The transmission units for wire linetransmission are FC E1/T1 and FXC E1/T1, whereas FC RRI and FXC RRI

are the microwave transmission units. The latter two are compatible with

Nokia MetroHopper and Nokia FlexiHopper microwave radios.

UltraSite

Nokia UltraSite EDGE BTS has many features and benefits, such as:

Nokia UltraSite EDGE BTS is light weight and compact and, with its

fullfrontal accessibility, can be installed just about anywhere.

The modular design of Nokia UltraSite EDGE BTS guarantees smooth

expansion and upgrades of base station equipment with minimal disturbanceto network operation. In addition, the BTS supports hot insertion of plug-in

units, which means that most units can be replaced during operation without

disrupting the BTS functions.

Nokia UltraSite EDGE BTS cabinets can be installed side by side and in

corners, which means less space is required.

Nokia UltraSite EDGE BTS fits into the corresponding Nokia Talk-family

BTS footprints. The operator does not need to alter any previous plans for

expansion. In addition, the BTS can be co-sited with Nokia Talk-family as an

upgrade cabinet.

Figure 5. UltraSite


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Table 1. Nokia base station features, summary

RF Characteristics Metrosite PrimeSite InSite Flexitalk Intratalk Citytalk UltE

Max. TRXs 4 1 1 2 6 6

Max. TRXs Special

Cabinet

12 12 1

Max. Sectors 4 1 1 1 4+4+4 4+4+4 36+

Max TX Power

(dBm)

30 38 22 42 42 42

Dynamic sensitivity

(dBm) single branch,

RBER2


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rD

R =2 2

E- field

H- field

Figure 6. Electrical and magnetic field vectors

At distances less than the far field distance (antenna near field), no reliable

signal measurements can be performed, since the electromagnetic field hasnot yet settled to its final and stable state. Signal strength measurements

therefore always are relative to an arbitrary reference point (e.g. 10m, 100m, 1

km...) from the antenna. The difference between signal power measured at the

reference point and the signal power input to the antenna is called the

minimum coupling loss. Typical values for coupling loss are in the order of 50

dB at 5..10m distance from the antenna.

Energy in an antenna only partly converts to electromagnetic waves.

Therefore the received energy is only a fraction of the radiated energy. The

received energy can only be measured at a reference distance from the

antenna. This distance is agreed to be the far field distance. The coupling

losses are approximately 50-60 dB for the first few meters. After that freespace propagation can be used.

2.2.2 Antenna Types

Many different types and mechanical forms of antennas exist. Each is

specifically designed for special needs.

In mobile communications the two main categories to consider are:

omnidirectional antennas:radiate with same intensity to all directions

(in azimuth) directional antennas:main radiation energy is concentrated to certain

directions

Omnidirectional antennas are useful in rural areas, while directional beam

antennas are preferable in urban areas. They provide a more controllable

signal distribution and energy concentration.

The most common antenna types are:


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Dipoles:the basic antenna type. Simple design, low gain,

omnidirectional radiation pattern.

Arrays:combination of many elementary arrays. High achievable

gains, special radiation pattern can be engineered. Active arrays usemany actively fed dipole elements. Passive arrays merely use the

reflecting properties of array elements.

Yagi antenna:Very popular passive array antenna. Widespread use as

TV-reception antenna. Very high gain and good directional effects.

Parabolic antenna:Used for microwave links, optical antennas and

satellite links. Very high gains and extremely narrow beamwidth. Most

commonly used for line-of-sight propagation paths. (satellites,

microwave links)

2.2.3 Antenna Characteris tics

Antennas can be characterised with a number of attributes:

Radiation pattern:the main characteristic of antennas is the radiation

pattern. The horizontal pattern (H-plane) describes azimuth

distribution of radiated energy. The vertical pattern (E-plane)

describes the energy distribution in elevation angle.

Figure 7. Horizontal and vertical antenna radiation patterns

Antenna gainis a measure for the antennas efficiency. Reference

antenna configuration to compare with is by convention the isotropic

antenna. Gain is measured usually in decibel above isotropic (dBi) or

in decibel above Hertz dipole (dBd). Hertz dipole has a gain of 2.2


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dB compared to the isotropic antenna, therefore dBd + 2.2 = dBi.

Antenna gain depends on the mechanical size of the antenna, the

effective aperture area, the frequency band and the antenna

configuration. Antennas for GSM1800 can achieve some 5...6 dB more

antenna gain than antennas for GSM900 while maintaining the samemechanical size. Antenna gain can be estimated by the formula:

G A w=4

2

where A is the mechanical size and w the effective antenna aperture

area.

NoteCatalogues usually show dBi values, since they are higher numerical values and

therefore look more impressive...

Antenna lobes:main lobe, side-lobes; ratio of main lobe to max. side

lobe is a measure for quality of radiation pattern

Half-power beamwidth:3-dB beamwidth; the angle (in both azimuth

and elevation plane), at which the radiated power has decreased by 3

dB with respect to the main lobe. Narrow angles mean good focusing of

radiated power (= larger communication distances possible)

Antenna downtilt(mechanical or electrical): directional antennas maybe tilted either mechanically or electrically in order to lower the main

radiation lobe.

By downtilting the antenna radiation pattern, field strength levels from

this antenna at larger distances can be reduced substantially. Therefore

antenna downtilting reduces interference to neighbouring cells while

improving spot coverage also. Two types of downtilting exist:

Mechanical downtiltingmeans that the antenna is pointed towards the

ground in the main beam direction. At the same time the back lobe is

uptilted.

Electrical downtiltinghas the advantage that the antenna pattern isshaped so that the main beam and the back lobe are downtilted. In order

to be able to control the interference situation it is better to use

electrical down tilting.

With omnidirectional antennas, mechanical downtilting is not

applicable, but only electrical. Electrical downtilting is performed by

internal slight phase shifts in the feeder signals to the elementary

dipoles of the antenna system.


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Figure 8. Radiation pattern of an antenna with electrical downtilt

5..8 deg

Figure 9. Mechanical downtilting

Polarisation:polarisation plane is the propagation plane of the

electrical field vector (by definition). Antennas are usually vertically

polarised. Cross-polarised antennas achieve some dB gain in signal

quality in environments where the radio wave is subjected to

polarisation shifts, e.g. by multipath propagation and reflection on

dielectric materials.

Antenna bandwidth:defined as the bandwidth, within which the VSWR

(Voltage Standing Wave ratio) is less than 1:2. Typical values for

antenna bandwidths are approx. 10% of the operating frequency.

Antenna impedance:maximum power coupling into antennas can be

achieved when the antenna impedance matches the cables impedance.

Antenna impedance depends on the design used. Impedance can be

trimmed to practically any value by micro strip stubs, coils and

capacitors. This is done by the antenna supplier and not relevant to the

network planner. Typical value is 50 Ohm.

Mechanical size:mechanical size is related to achievable antenna gain.

Large antennas provide higher gains, but also need more care in


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deployment (optical impact!) and apply higher torque to the antenna

mast (static). Wind load and icing of antennas in winter may cause

static problems to the mast. Usual values for wind velocities are

assumed at 150 km/h or 200 km/h.

2.2.4 Coupling Between Antennas

Antenna radiation pattern will become superimposed when distance between

antennas becomes too small. This means the other antenna will mutually

influence the individual antenna patterns.

As a rule of thumb, 5 ..10 horizontal separation provides sufficient

decoupling of antenna patterns. The exact distance needed depends on the

individual radiation patterns.

As vertical radiation patterns often have very much narrower half-powerbeamwidth, the vertical distance needed for decoupling is also much smaller.

As the rule of thumb, 1vertical separation is sufficient in very most cases.

main lobe

5 .. 10

1

Figure 10. Horizontal and vertical separation

2.2.5 Installation Examples

Antenna installation configurations depend on the operators preferences, if

any. It is important to keep sufficient decoupling distances between antennas.

If TX and RX direction use separated antennas, it is advisable to keep a


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horizontal separation between the antennas in order to reduce the TX signal

power at the RX input stages.

Recommended decoupling

TX - TX: ~20dB

TX - RX: ~40dB

Horizontal decoupling distance depends on

antenna gain

horizontal rad. pattern

Omnidirectional antennas

RX + TX with vertical separation (Bajonett)

RX, RX div. , TX with vertical separation (fork)

Vertical decoupling is much more effective

0,2m

omnidirectional.: 5 .. 20mdirectional : 1 ... 3m

Figure 11. Antenna coupling

Figure 12. Antenna installation examples

2.2.6 Nearby Obstacles Requirement

Nearby obstacles are those reflecting or shadowing materials that can obstruct

the radio beam both in horizontal and vertical planes. When mounting the


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antenna system on a roof top, the dominating obstacle in the vertical plane is

the roof edge itself and in the horizontal plane, obstacles further away, e.g.

surrounding buildings, can act as reflecting or shadowing material.

It is possible that the antenna beam will be distorted if the antenna is too closeto the roof. In other words, the antenna must be mounted at a minimum height

above the rooftop or other obstacles. As a practical planning / installation rule,

the first Fresnel zone (vertical plane) must be kept clear. The clearance is

between the bottom of the antenna and the most dominant obstacles. As a rule

of thumb, in the horizontal plane the 3dB beamwidth must be clear within

150m.

Figure 13. Required height clearance from the antenna to the edge ofthe rooftop


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h h

Figure 14. Antenna tilting near an edge of the rooftop

Antenna downtilt affects previous results. The following graph shows how the

clearance requirement changes when antenna downtilt varies from 0 to 6

degree.

Height Clearance vs Antenna Tilt

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

9,0

5 10 15 20 25 30 35 40 45 50

Distance to the roof edge d (m)

h (m)

From 0up to 6

down tilt

Figure 15. Height clearance versus antenna tilt

If antennas are wall mounted, a safety margin of 15between the reflecting

surface and the 3-dB lobe should be guaranteed, see Figure 16.


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Figure 16. Horizontal clearance

2.3 Diversity Techniques

Diversity techniques are based on the fact that receiving multiple uncorrelated

copies of the same signal, at the same or delayed time, can reduce fast fading

dips. When two received signals are combined, the achieved signal quality is

better than either of the partial signals separately.There are different diversity reception schemes (see Figure 17): both the base

station and the mobile station implement time diversity already by

interleaving. Frequency diversity can be achieved with frequency hopping:

since fast fading is frequency dependent, many frequencies are quickly and

cyclically hopped so that if one frequency is in a fading dip, it is just for a

very brief time. Traditionally two base station receiver antennas have been

separated horizontally (usually) or vertically (seldom) to create space

diversity. In urban environment, the same diversity gain can be achieved by

using polarisation diversity: signals are received using two orthogonal

polarisations at the reception end.

In the mobile radio channel multipathpropagationis present. The delayedand attenuated signal copies can be combined in a proper way to increase the

level of the received signal (multipath diversity). In GSM it is performed by

an equaliser, while in W-CDMA (Wideband-CDMA) a so called "rake

receiver" is utilized.


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Time diversity

Frequency diversity

Space diversity

Polarisation diversity

Multipath diversity

Transmit the same signal at leastwice (with time delay t)

Transmit the same signal on at ltwo different frequency bands

multiple antennas

crosspolar antennas

equaliser,rake receiver

t

f

Figure 17. Diversity techniques

The most used methods in cellular network planning are space and

polarisation diversity, as far as base station antennas are concerned.

2.3.1 Space Diversity

Space diversity is a traditional diversity method, especially used in

macrocells. Spatial antenna array separation causes different multipath lengths

between a mobile station and a base station. Partial signals arrive at the

receiving end in different phases. The two antenna arrays must be separated

horizontally in order to achieve uncorrelated signals. Space diversity performs

very well with macrocells in all environments, giving diversity gain of about

4-5 dB.In microcells, the large antenna configurations are not often possible due to

site acquisition and environmental reasons. An

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